Traders said mostly short-term investors were active in the market and the move might reverse soon, especially if a Spanish auction of short- and medium-term debt on Thursday disappoints.
The Federal Reserve concludes a two-day policy meeting later and the market has high expectations that it may extend its "Operation Twist" bond-buying programme that aims to push down long-term borrowing costs by selling short-term securities to buy longer-term ones.
Traders said the market was also expecting a dovish tone from the Fed, possibly signalling further easing in the future.
Safe-haven Bund futures were last 29 ticks lower at 141.07, having earlier hit a six-week low of 140.82. Ten-year German cash yields were 4 basis points higher at 1.57 percent.
"The market is betting (Fed Chairman Ben) Bernanke would ride to the rescue here with some form of Fed magic," said Commerzbank interest rate strategist David Schnautz, adding that the break below the 50-day moving average in the Bund future around 141.55 accelerated the sell-off.
One trader said the prospect of Greece's pro-bailout parties forming a coalition later in the day and that a European agreement may soon be reached to rescue Spain's ailing banks were "bits and pieces giving a bid to the periphery".
A second trader said talk about the euro zone's rescue funds stepping in to buy Spanish and Italian debt was also supporting those bonds. The idea was put forward by Italy at a Group of 20 summit in Mexico on Tuesday.
This helped 10-year Spanish yields edge down. But they remained close to 7 percent - a level closely watched by investors as Ireland and Portugal were eventually forced out of debt markets after their yields rose beyond there.
AUCTIONS
Spanish short-term bonds underperformed the rest of the curve before sales of 2014, 2015 and 2017 bonds on Thursday. Madrid paid its highest average cost since the launch of the euro to sell 12-month paper on Tuesday.
As investors believe more aid may be needed to solve Spain's problems than the agreed rescue package of up to 100 billion euros for its banks, every Spanish debt auction is seen as a cliffhanger.
"I don't know about this risk rally, we have a Spanish auction tomorrow," the second trader said.
Germany will sell up to 5 billion euros of two-year bonds later on Wednesday, with the auction expected to find sufficient demand after a rise in yields in recent days.
Two-year bonds yielded 0.089 percent after starting the month in negative territory as investors flocked into German debt fearing the euro zone might collapse under the weight of its Greek and Spanish problems.
"The auction should be an easy exercise," Commerzbank's Schnautz said. "As the market makes more room (for the new bonds) we may actually touch 10 basis points, which these days is almost a bargain."